Because: "users" is not added to /dev/sda1 on boot, only the device owner (root) mounts USB. I want non-root users to mount USB pens and not have this result:
$ mount /dev/sda1 /mnt/flash
mount: only root can do that
$ mount /dev/sda /mnt/flash
mount: only root can do that

Ok, now tried same thing with USB:
$ mount /mnt/flash
mount: I could not determine the filesystem type, and none was specified
$ mount -t auto /mnt/flash
mount: only root can do that
$ mount -t vfat /mnt/flash
mount: only root can do that

Grrrr! So, I tried as suggested from my Flash doc for unix mount:
- mkdir /mnt/USB
- edit /fstab using /dev/sda (paritition 0, and not sda1), had to ajust and add "users"
/dev/sda /mnt/USB auto noauto,users,owner,kudzu 0 0
Pretty much the some thing as for /mnt/flash, huh!